In a fiber optic system, a light source emits light pulses that travel through optical fibers to transmit data. The light source and the optical fiber must be accurately aligned to maximize the coupling efficiency. The coupling efficiency is a measurement of how much light transmitted by the light source is actually received by the optical fiber.
One of the methods used to achieve alignment between the light source and the optical fiber is known as active alignment. In active alignment, the light source is turned on while its aperture is aligned to the receiving end of the optical fiber. The light source and receiving end of the optical fiber are adjusted while the transmitting end of the optical fiber is monitored by a light detector. The light detector measures the amount of light passing through the optical fiber. When the light received is at its maximum, the light source and the optical fiber are at an optimal alignment, at which point the optical fiber and light source are fixed into place.
Active alignment is time consuming and therefore expensive. Thus, it is desirable to produce components that can be aligned in assembly without turning on the light source or using a light detector. Such a process is known as passive alignment.
Passive alignment has its own drawbacks. The apertures of the light source and the optical fibers are very small, and the focal lengths of the lenses impose their own strict requirements on the location of each component. For example, FIG. 1 shows a prior art optical system 51. The prior art optical system 51 includes a light source 53, coupling optics 55, and an optical fiber 57. In conventional optical transmitters, the coupling optics 55 is a single unit having a first lens surface 59 and a second lens surface 61. The first lens surface 59 has a focal length of F1. The second lens surface 61 has a focal length of F2. The coupling optics 55 receives light from the light source 53 and focuses it onto the optical fiber 57. To achieve this, the optical axis of the light source 53 must be aligned with the optical axis of the first lens surface 59, and the optical axis of the second lens surface 61 must be aligned with the optical axis of the optical fiber 57. Furthermore, the light source 53 must be at a distance F1 from the first lens surface 59. Finally, the optical fiber 57 must also be at a distance F2 from the second lens surface 61.
The requirements of prior art optical system 51 leave very little tolerance during passive alignment. Consequently, expensive precision instruments are required to carefully measure, position, and place each component such that the light from the light source will be focused exactly on the target aperture of an optical fiber. Therefore, it is desirable to produce components that have greater tolerance so that passive alignment can be achieved with greater ease.